On June 8, 2000, the
U.S. Environmental Protection Agency (EPA) and Dow AgroSciences, reached
an agreement to stop the sale of most home, lawn and garden uses for chlorpyrifos
because of its health risks to children.

USAGE

Chlorpyrifos (trade
names include DursbanTM and LorsbanTM) is one of the most widely used
insecticides in the U.S., with 20 to 24 million pounds applied annually,
and has been linked to thousands of pesticide poisoning incidents. This
Dow AgroSciences, previously DowElanco, product is a broad-spectrum chlorinated
organophosphate insecticide.

Chlorpyrifos is registered
for the control of cutworms, corn rootworms, cockroaches, grubs, flea
beetles, flies, termites, fire ants, mosquitoes, and lice. It is used
as an insecticide on grain, cotton, fruit, nut, and vegetable crops, as
well as on lawns and ornamental plants. It is also registered for direct
use on sheep and turkeys, for horse site treatment, dog kennels, domestic
dwellings, farm buildings, storage bins, and commercial establishments.

TOXICITY

Chlorpyrifos is acutely
toxic to rats with an LD50 of 135 mg/kg.

Chlorpyrifos poisoning
may affect the central nervous system, the cardiovascular system and the
respiratory system, as well as irritate the skin and eyes. Acute exposure
can result in numbness, tingling, incoordination, dizziness, vomiting,
sweating, nausea, stomach cramps, headache, vision disturbances, muscle
twitching, drowsiness, anxiety, slurred speech, depression, confusion
and in extreme cases, respiratory arrest, unconsciousness, convulsions,
and death. Persons with respiratory ailments, recent exposures to cholinesterase
inhibitors, cholinesterase impairment, or liver malfunction are at increased
risk from exposure to chlorpyrifos. Chlorpyrifos has also been linked
to Multiple Chemical Sensitivity.

Chlorpyrifos is linked
to delayed peripheral neuropathy (degenerative lesions of sensory, motor,
or reflex nerves). Italian researchers published a disturbing report of
an acute chlorpyrifos-poisoning episode, resulting in delayed peripheral
neuropathy. There are also reports of EEG (brainwave) pattern, sleep pattern
and behavioral changes lasting over a year following exposure to organophosphate
insecticides.

Organophosphates are
cholinesterase inhibitors. They bind irreversibly to the active site of
an enzyme essential for normal nerve impulse transmission, acetylcholine
esterase (AchE), inactivating the enzyme. A common diagnostic for poisoning
is to assay for blood AchE depression. Repeated or prolonged exposure
to organophosphates may result in the same effects as acute exposure,
including delayed symptoms.

A 1996 study of children exposed to chlorpyrifos in utero found that extensive
and unusual patterns of birth defects, including brain, nervous system,
eyes, ears, palate, teeth, heart, feet, nipples, and genitalia. Published
literature and EPA documents contain reports that identify similarities
in defects found in test animals and children exposed to chlorpyrifos.

In 1997, EPA Office
of Pesticide Programs', Health Effects Division reported that chlorpyrifos
is one of the leading causes of acute insecticide poisoning incidents
in the U.S. One U.S. News & World Report investigation, "The
stuff in the backyard shed," (November 8, 1999, page 64-68) reports
that since 1992, Dow AgroSciences and predecessor manufacturers have sent
approximately 7,000 reports of chlorpyrifos-induced reactions to EPA.
The agency, according to the report, suspects chlorpyrifos in 17,771 incidents
reported to the U.S. Poison Control Centers between 1993 -96.

In 1999, EPA's Office
Pesticide Programs, Health Effects Division, reported that four pesticides,
phosmet, proetamphos, chlorpyrifos, and dimethoate, had consistently high
rankings in being responsible for symptoms, health care facility visits,
hospitalizations, and fatal outcomes in adults and children. These four
organophosphate pesticides are responsible for 90% of pesticide exposures
reported in children under six to the Poison Control Centers around the
country from the 1993-1996. The report also stated that "children,
under six exposed to organophosphates, were three times more likely to
be hospitalized, five times more likely to be admitted for critical care,
and four times more likely to have experienced a major medical outcome
or death, than if exposed to some other, non organophosphate, pesticide."

In animals, chlorpyrifos
transforms to chlorpyrifos-oxon, which is about 3000 times as potent against
the nervous system as chlorpyrifos itself.

ECOLOGICAL EFFECTS

There is a wide range
of adverse environmental effects linked to chlorpyrifos, include toxicity
to beneficial insects, freshwater fish, other aquatic organisms, bird,
a variety of plants, soil organisms, and domestic animals. It has been
shown to bioaccumulate in fish and synergistically react with other chemicals.
Chlorpyrifos may be toxic to some plants, such as lettuce.

ENVIRONMENTAL FATE

There are few data
available on air levels or surface residues following application either
as a termiticide or for indoor pest control. The American Conference of
Governmental Industrial Hygienists recommends an occupation air level
guideline of 200-micrograms/cubic meter (µg/m3) for a forty-hour
workweek. The National Academy of Sciences proposed a 10µg/ m3 air
level for the general public, while the New York State Department of Health,
with a recommendation to use a 100-fold safety factor, would arrive at
an air limit of 0.49µg/m3 for children, and 1µg/ m3 for adult
exposures.

Work by Fenske et
al. found that air levels 24 hours after a proper application were as
high as 30µg/ m3 in the infant breathing zone, 60 times EPA's limit.
Furthermore, Fenske calculated that infant exposure through inhalation
and skin absorption might be more than five times the human threshold
for acute effects (No Observable Effect Level). The researchers state
that, "Exposures to cholinesterase inhibiting compounds following
properly conducted broadcast applications could result in doses at or
above the threshold of toxicological response in humans."

In common with most
organophosphates, chlorpyrifos has a relatively short biological half-life,
roughly 24 hours in blood, and 60 hours in fat (assuming that multiple
or continuous exposure does not occur) and it has shown no potential to
bioaccumulate in mammals. Its half-life indoors is estimated to be 30
days. Various studies of different treatment methods show chlorpyrifos
present up to eight years post application. A 1998 study found that chlorpyrifos
accumulated on furniture, toys, pillowcases, and other sorbant surfaces
up to two weeks after indoor application.

Chlorpyrifos is sensitive to light, alkaline substances such as bleach,
and microbial degradation. Eventually, it degrades completely to carbon
dioxide and water. The half-life of chlorpyrifos in water is relatively
short, from a few days to two weeks. It adsorbs readily to sediments and
organic matter, its half-life in soil is usually between 60 and 120 days,
but can range from 2 weeks to over one year, depending on the soil type,
climate, and other conditions.
Residues remain on plant surfaces for approximately 10 to 14 days. Data
indicate that this insecticide and its soil metabolites can accumulate
in certain crops.

The granular formulation
of chlorpyrifos has been found to be more persistent and may persist as
long as 180 days. The major biological metabolite and environmental breakdown
product is 3,5,6-trichloro-2-pyridinol (TCP).

According to an EPA
memorandum, groundwater monitoring at a Cape Cod golf course detected
TCP in samples. Reports from the USDA Southern Forest Experimental Station
note that the termiticide formulation is effective against termites for
more than 15 years.

Chambers, J., et al.
1993. "Inhibition of patterns of brain acetylcholinesterase and hepatic
and plasma alesterases following exposures to three phosphorothionate
insecticides and their oxons in rats." Fund. Appl. Toxicol. 21:111-119.